Photo-refractive keratectomy (PRK), laser-assisted in situ keratomileusius (LASIK), and laser-assisted subepithelial keratomileusius (LASEK) are procedures performed on patients to improve a patient's vision by ablating intrastromal corneal tissue. PRK and LASIK procedures involve forming a flap of corneal tissue to expose the corneal stroma of an eye undergoing a surgical procedure. Typically, a corneal flap formed during a PRK or LASIK procedure has a thickness greater than 100 micrometers, for example, from about 130 micrometers to about 180 micrometers. Thus, a cut is made into the corneal stroma at a depth greater than 100 micrometers from the anterior or exterior surface of the eye. In comparison, the LASEK procedure involves forming a flap of corneal epithelium or a corneal epithelial flap. The LASEK procedure involves making a cut about 55 micrometers deep (e.g., a depth equal to or slightly greater than the thickness of a healthy adult corneal epithelium), and applying ethanol to loosen the corneal epithelial tissue and facilitate separation of the corneal epithelial flap from the underlying Bowman's membrane.
Examples of microkeratomes and related components useful for cutting corneal tissue in ablative procedures include those described in U.S. Pat. Nos. 5,496,339; 5,690,657; 6,071,293; and U.S. Patent Publication No. 20050251185.
Corneal onlays have been proposed as an alternative to these ablative procedures. A corneal onlay may be understood to be a corneal implant, and more specifically, an implantable ocular device or lens, that is placed on or anterior to Bowman's membrane, for example, between Bowman's membrane of the cornea of an eye and the corneal epithelium of the eye. Since corneal onlays are devices implanted into the eye of a patient, corneal onlays provide the opportunity to improve a patient's vision for long periods of time, but also provide a reversible procedure to correct refractive error. These procedures may result in improvements in a patient's vision without the need for spectacles or contact lenses.
Previously described approaches of using corneal onlays required complete removal or abrasion of the corneal epithelium to expose the underlying Bowman's membrane. It was postulated that placement of a corneal onlay on a deepithelialized Bowman's membrane would be helpful in improving a patient's vision. However, such procedures required corneal epithelial cells to grow and migrate over the corneal onlay, and the procedures presented significant issues of corneal epithelial undergrowth beneath the implanted corneal onlay. More recently, procedures for implanting corneal onlays have been proposed which include implanting a corneal onlay under a corneal epithelial flap or in a corneal epithelial pocket. For example, see U.S. Patent Publication Nos. 20030220653; 20050070942; 20050080484; 20050124982; and 20060052796; and International Patent Publication Nos. WO 2005/030102; WO 2005/049071; and WO 2006/007408.
While covering corneal onlays with corneal epithelial flaps provides some advantages, the corneal onlays may be prone to becoming decentered after the surgical procedure. Corneal epithelial pockets, that is pockets formed between the corneal epithelium and the corneal Bowman's membrane, can be effective in reducing decentration of the implanted corneal onlay after the surgical procedure, among other things.
A need remains for new systems and system components that are effective in forming a pocket between a corneal epithelium of an eye of a patient and the underlying Bowman's membrane. In other words, an existing problem relates to forming a corneal onlay implantation site which is associated with reduced decentration of an implanted corneal onlay compared to an implanted corneal onlay located beneath a corneal epithelial flap. In addition, a need remains for systems and system components which can separate substantially all of the corneal epithelium from the underlying Bowman's membrane to provide an implantation site that is free of epithelial cells. It can be understood that another existing problem relates to forming a corneal epithelial pocket to provide a Bowman's membrane without corneal epithelial cells that can negatively affect a corneal onlay placed in the pocket.